Field
The present invention relates to an air fuel ratio controlling apparatus, and particularly to an air fuel ratio controlling apparatus suitable for use with, for example, a vehicle such as a motorcycle or the like which includes an internal combustion engine therein.
Description of the Related Art
For example, in a system wherein exhaust gas of an internal combustion engine of an automobile or the like is purified by a catalytic apparatus and then discharged, it is desired from a point of view of environmental protection that the air fuel ratio of exhaust gas of the engine be controlled to a suitable air fuel ratio so that a good exhaust gas purification capacity may be exhibited.
As a technique for carrying out such air fuel ratio control as described above, for example, an air fuel ratio controlling apparatus disclosed in Patent Document 1 (Japanese Patent Number 3373724) is available.
Patent Document 1 discloses an air fuel ratio controlling apparatus configured such that, in order to cancel a displacement of a fuel injection amount calculated from a fuel injection amount map (in which an engine speed, a throttle opening, a negative pressure and so forth are used as parameters) for determining a fuel injection amount of the engine from a target air fuel ratio, a correction coefficient is superposed on the fuel injection amount.
In particular, a LAF sensor which converts an oxygen concentration or air fuel ratio of exhaust gas into a signal having a level which increases in proportion to the oxygen concentration over a wide range of the oxygen concentration is installed on the upstream of a catalytic apparatus or purifier disposed in an exhaust pipe of the engine while an oxygen sensor/air fuel ratio sensor is provided on the downstream of the catalytic apparatus. Then, a predicted value of the air fuel ratio after the catalyst is calculated using a detected value of the LAF sensor and a correction coefficient is determined, for example, by a sliding mode controller using the predicted value.
Since the LAF sensor is expensive, there is a desire to eliminate the LAF sensor provided on the upstream of the catalytic apparatus to reduce the cost of the system or from a reason that there is a restriction to the disposition space in a motorcycle or the like.
However, since an output value (SVO2) of the oxygen sensor which is a target value of the emission is converged to a target value based on the output value (SVO2) which is an input value to a sliding mode controller (SMC) which models intake and exhaust of the engine, where the LAF sensor is not installed on the upstream of the catalytic apparatus, the air fuel ratio before the catalyst cannot be measured. Therefore, the tolerance and the time-dependent variation of the engine and prediction of an injection error or the like of a fuel injection valve in the model of the engine cannot be monitored, and there is the possibility that the prediction range of the predicted value for the output value (SVO2) may be expanded and much time may be required for the convergence to the target value by the sliding mode controller (SMC).
Further, since there is a restriction in adjustment also to the convergence gain of the sliding mode controller (SMC), a prediction error of a predicted value of the output value (SVO2) may not be eliminated and the output value (SVO2) may not be able to be converged to the target value.